Macrolides, such as azalides, are a class of antibiotics which contain a many-membered lactone ring to which are attached one or more deoxy sugars. Macrolides are generally bacteriostatic, but have been shown to be bacteriocidal in high concentration against very susceptible organisms. Macrolides are most effective against gram-position cocci and bacilli, although they do possess some activity against some gram-negative organism. Macrolides exert their bacteriostatic activity by inhibiting bacterial protein synthesis by binding reversibly to the 50 S ribosomal subunit. ("Goodman & Gillman's the Pharmacological Basis of Therapeutics," 9th ed., J. G. Hadman & L. E. Limbird, eds., ch. 47, pp. 1135-1140, McGraw-Hill, New York (1996)).
The macrolides as a class are colorless and usually crystalline. Macrolides, such as azalides, are generally stable in near neutral solution, but they only have limited stability in acid or base solutions. The reason for this is because the glycosidic bonds hydrolyze in acid and the lactone ring saponifies in base ("Principles of Medicinal Chemistry," 2nd ed., W. F. Foye, ed., ch. 31, pp. 782-785, Lea & Febiger, Philadelphia (1981)). Hence, there is a need to prepare stable, water miscible pharmaceutical or veterinary compositions for parenteral, e.g., intravenous, intramuscular, subcutaneous, administration of macrolide antibiotics.
Macrolides as a class, which include azalides, are soluble in many organic solvents but are only slightly water soluble. Solutions of macrolides in organic solvent systems are used in human and veterinary practice for administration by the intramuscular and subcutaneous routes. These solutions cannot be used for intravenous administration because the macrolides precipitate when the solution is introduced into an aqueous medium as into body fluids. Aqueous solutions of salts of macrolides can be prepared but such solutions have such limited stability as to be limited to use for only a short time period after preparation.
A water miscible solution of macrolides, including azalides, which would be stable for an extended period of time would be of great value to both the medical and veterinary professions. It could be used for intravenous administration to rapidly provide therapeutic blood levels for more effective treatment of infectious diseases. A water miscible solution would also allow for more rapid absorption from intramuscular and subcutaneous injection sites leading to higher concentrations in body fluids and more effective control of infectious diseases. Such a solution would also be useful for oral administration to poultry and swine in their drinking water.